Clinical, Pathologic, and Hemodynamic Considerations in Coarctation of the Aorta Associated with Ventricular Septal Defect

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Abstract
The association of coarcta-tion of the aorta with ventricular septal defect does not modify the accuracy of recognition of the septal defect. But the defect does provide an alternative pathway for the escape of blood from the left ventricle, thereby tending to minimize hypertension in the upper part of the body. Along with this, the radiologic evidence of coarctation is minimized or obscured and ecg changes resemble those in isolated ventricular septal defect. A substantial pressure gradient between upper and lower body, however, is a reliable indication of the existence of a severe degree of coarctation. These considerations are not importantly affected by coexistence of a patent ductus arteriosus joining the aorta above the coarctation. Should a ductus join the aorta at the site of coarctation, it will either have the effect of bypassing the coarctation or will behave functionally as though it joined the aorta proximal or distal to the obstruction. When in the presence of a ventricular septal defect and coarctation of the aorta a large patent ductus arteriosus joins the aorta beyond the coarctation, the pressure above and below the coarctation may be almost the same. The ventricular septal defect tends to equalize the systolic pressure in the two ventricles, so that the pressures in the pulmonary artery and descending aorta are very similar. The lower body may be supplied partially or completely by blood from the pulmonary artery. The oxygen saturation of blood in the pulmonary artery is abnormally high because of the shunt through the ventricular septal defect, and so the difference in oxygen saturation between the upper and lower body may be very small. In consequence, both the coarctation and the patent ductus may escape recognition on clinical grounds. The demonstration at cardiac catheterization of a difference in arterial oxygen saturation between the upper and lower body and the confirmation by dye-dilution technics or angiocardiography of the coexistence of a left-to-right ventricular shunt and a right-to-left arterial shunt establish the presence of obstruction between the outflow tract of the left ventricle distal to the ventricular septal defect and the entry of the ductus into the aorta. The hemodynamic situation produced when ventricular septal defect and coarctation of the aorta form part of more complicated combinations of defects is discussed briefly.